Know what was the process of mapping corrosion in aircraft belonging to the Colombian Air Force.
by: Liliana Isabel Rodríguez González*
The corrosion mapping seeks to estimate the degree of atmospheric corrosivity present in the units of the Colombian Air Force, FAC, by means of coupons with the same characteristics of the material used in the structures with which the aircraft are made. These coupons will be subjected to a weight loss analysis with which it will be possible to determine the aggressiveness of the environment to which the structures of the aircraft in the FAC units are exposed; managing to determine also the effectiveness of corrosion and paint inhibitors that are currently used for these aircraft.
For the elaboration of the coupons that make up the corrosion mapping, the ASTM international (Association Testing Materials)1, NACE International (International Association of Corrosion Engineers)1, and ISO (International Standard Organization) standards were taken into account, as well as the elaboration of the rack (support of the coupons), its inclination and dimensions. That is, its approach follows the same procedure of any of the international projects that are carried out following standard procedures, in order to obtain standardized information comparable to the standards of the standards used.
In total there are seventy-six coupons, 38 of which are different from each other in alloy and thickness; however, these are replicas of the other 38, for the purpose of comparing results. These coupons represent the composition of the different structures of which an aircraft is composed. See photo 1.
Procedure
This project lasted two years. The first year corresponded to the installation of the mapping in the different aerial units and the second was the time of permanence of the mapping outdoors, counted once the 12 mapping were finished installing in all the aerial units, which bring together all the Colombian geographical areas (Bogotá, Madrid-Cundinamarca, Cali, Villavicencio, Melgar, Rionegro-Antioquia, Barranquilla, San Andrés, Yopal, Caquetá, Vichada, Puerto Salgar).
The success of the project depended on the monitoring of each of the test stations, the analysis of the data and the proper use of corrosion kinetics formulas and their interpretation.
The basic procedure consisted of making direct measurements on the coupons with equipment as established by the ASTM, NACE standards, with the equipment in photo 2.
Once the data was taken, they were stored in Excel, where the calculations of the corrosion kinetics were also made; that is, the training speeds (Entered by the researcher). Finally, at the end of the year, the results were interpreted by means of the iso 9223 standards: Corrosivity Classification, ISO 9224: Guide to values and corrosivity categories, ISO 9225: Pollution measurement and ISO 9226: Determination of the corrosion rat in standard specimens.
The results will translate into improved CPCP corrosion programs for FAC aircraft, and will be different in each geographic region.
Diagnosis
Complementing the corrosion mapping project and taking into account that all environmental factors that affect corrosion must be evaluated, it was detected that aircraft washing water must be of good quality and must meet parameters set by the USAF (American Air Force) and contemplated in O.T 1-1-691 (Technical Order), for which in the installation stage of the racks (coupon bank) water samples were taken and each of its parameters (pH, conductivity, total solids, biological oxygen demand, chlorine content, iron, nitrites, calculation of the corrosivity index or langelier) were analyzed, with the equipment in photo 3.
Figure 1 shows the corrosion velocities of each of the Colombian Air Force Air Bases per g/m2.
The results indicate that the site of greatest corrosivity is CACOM-3, since it is close to the sea with a distance to this of 0.010 Km, which indicates chloride atmosphere. In second place is GAORI, as it is an arid area; GACAR obtained the third place for being an Island and finally CACOM-4 for having in its atmosphere chlorine from the treatment of the pools.
The alloys with the highest corrosion rates are: 7075T6 aluminum thickness 0.040", 2024T3 0.040" and 4130 steel.
The results obtained will change the corrosion control programs of FAC aircraft.
References
1. ASM HANDBOOK VOLUME 13th: Corrosion: Fundamentals, Testing, and Protection
* Chemical Engineer. Directorate of Engineering and Maintenance of the Colombian Air Force. [email protected]
